The present invention generally relates to wireless communication networks, and particularly relates to base station power control.
Wireless communication networks typically use one or more power control mechanisms on the forward and reverse links. For example, in Code Division Multiple Access (CDMA) networks, base stations transmit power control commands to each mobile station to control the reverse link interference contribution of each mobile station. Such control commonly includes both “inner” and “outer” control loops. The inner control loop for a given mobile station is driven by the signal strength or a related parameter of the mobile station's reverse link transmit signal received at one or more base stations. More particularly, a base station supporting the mobile station on the reverse link compares the received signal strength of the mobile station's signal to a corresponding target strength and transmits up or down power control commands to the mobile station depending on whether the received strength is above or below the target.
A typical outer loop control mechanism then adjusts the value of that target upward or downward depending on the Frame Error (or Erasure) Rate (FER) of traffic frames received from the mobile station. For example, if the FER is below one percent, the target is adjusted downward, and if the FER is above one percent, the target is adjusted upward. Typically, the outer loop control runs more slowly than the inner loop control. For example, in CDMA networks based on the IS-2000 standards, inner loop power control runs at 800 Hz and outer loop power control runs at 50 Hz or less.
Similar control mechanisms are used on the forward link for selected transmissions to the mobile stations. For example, the forward link transmit powers allocated to the traffic channels of the mobile stations are adjusted upward or downward based on power control commands returned to the base station by the mobile stations. However, certain signals transmitted by or to the network typically have no direct power control feedback available. For example, in CDMA networks using common power control channels to transmit power control bits to individual mobile stations in time multiplexed fashion, there may be no direct feedback from the mobile stations to indicate whether the power control bits are being sent at the appropriate power.